Nearly forty million Americans now use a cellular telephone, and another seven million or so are expected to subscribe this year. Cellular telephone boutiques and kiosks are a fixture in nearly every mainstreet and mall in the United States. Cellular telephone sales have increased faster than those of facsimile machines, subscriptions to cable television, and video cassette recorders.
As the use of cellular telephones has increased, customers have come to expect ever greater convenience. The most critical feature in a cellular telephone is the battery. Cellular telephone users surveys have indicated that what users care about above all else is talk time. In order to increase their ability to chat on the telephone, users often carry spare batteries with them. However, there is often no immediate way to determine, or remember, whether or not a spare battery is charged or discharged. Therefore, there is a need for a system for determining immediately whether a battery is charged or discharged.